The invention of the present application relates to a semiconductor device having a circuit which is configured of thin film transistors (hereinbelow, termed xe2x80x9cTFTsxe2x80x9d), and a method of fabricating the semiconductor device. By way of example, it relates to an electrooptical device which is typified by a liquid crystal display panel, and an electronic equipment in which such an electrooptical device is installed as a component.
Incidentally, here in this specification, the xe2x80x9csemiconductor devicexe2x80x9d is intended to signify general devices which can function by utilizing semiconductor properties, and electrooptical devices, semiconductor circuits and electronic equipment are all the semiconductor devices.
In recent years, notice has been taken of technology wherein thin film transistors (TFTs) are constructed using a semiconductor thin film (having a thickness on the order of severalxcx9ca few hundred nm) which is formed on a substrate having an insulating surface. The TFTs are extensively applied to ICs and electron devices such as electrooptical devices, and it is especially hurried to develop them as the switching elements of an image display device.
Hitherto, liquid crystal display devices have been known as image display devices. The liquid crystal display device of active matrix type has come to be often employed because an image of higher definition than by the liquid crystal display device of passive type can be obtained. In the active matrix type liquid crystal display device, a display pattern is formed on a screen by driving pixel electrodes arranged in the shape of a matrix. More specifically, voltages are applied between selected ones of the pixel electrodes and ones of counter electrodes corresponding to the selected pixel electrodes, whereby a liquid crystal layer interposed between the pixel electrodes and the counter electrodes is optically modulated, and the optical modulation is recognized as the display pattern by an observer.
The applications of such an active matrix type liquid crystal display device have widened, and a higher definition, a higher aperture efficiency and a higher reliability have been more required together with the larger area of a screen size. Besides, enhancement in productivity and reduction in cost have been more required at the same time.
In the prior art, an amorphous silicon film is suitably employed as an amorphous semiconductor film for the reason that it can be formed on a substrate of large area at a low temperature of or below 300xc2x0 C. Also, TFTs of inverse stagger type (or bottom gate type) each having a channel forming region formed of an amorphous semiconductor film are often employed.
Heretofore, a liquid crystal display device of active matrix type has been high in its manufactural cost for the reason that TFTs have been fabricated on a substrate by using, at least, five photo-masks in accordance with photolithographic technology. In order to enhance a productivity and to enhance an available percentage, decreasing the number of steps is considered as effective means.
Concretely, it is necessary to decrease the number of photo-masks required for the manufacture of TFTs. The photo-mask is employed for forming a photoresist pattern to serve as the mask of an etching step, over a substrate in the photolithographic technology.
Using each of the photo-masks, steps such as coating with a resist, pre-baking, exposure to light, image development and post-baking are performed, and steps such as the formation and etching of a film and further steps such as stripping off the resist, washing and drying are added as the preceding and succeeding steps of the first-mentioned steps. These steps are complicated, and have been problematic.
Moreover, since the substrate is an insulator, static electricity has been generated by friction etc. during the manufacturing process. When the static electricity is generated, short-circuiting arises at the intersection part of wirings laid over the substrate, or the TFTs are deteriorated or destroyed by the static electricity, so that display defects or degradation in an image quality have/has occurred in the liquid crystal display device. In particular, during the rubbing of liquid crystal orientation processing which is performed in the manufacturing process, the static electricity appears and has been problematic.
The present invention consists in replying to such problems, and in a semiconductor device typified by a liquid crystal display device of active matrix type, it has for its object to decrease the number of steps for fabricating TFTs, thereby to realize reduction in a manufactural cost and enhancement in an available percentage.
Also, it has for its object to provide a structure capable of solving the problem of the destruction of TFTs or the characteristics deterioration thereof ascribable to static electricity, and a method of fabricating the structure.
In order to solve the problems, according to the present invention, each gate wiring is initially formed by a first photo-mask.
Subsequently, a gate insulating film, a non-doped amorphous silicon film (hereinbelow, called xe2x80x9ca-Si filmxe2x80x9d), an amorphous silicon film which contains an impurity element bestowing the n-type (hereinbelow, called xe2x80x9cn+a-Si filmxe2x80x9d), and an electrically-conductive film are formed in succession.
Subsequently, an active layer, a source wiring (including a electrode) and a drain electrode which are made of the a-Si film are patterned and formed by a second photo-mask.
Thereafter, a transparent electrically-conductive film is formed, whereupon a pixel electrode made of the transparent conductive film is formed by a third photo-mask. Further, a source region and a drain region which are made of the n+a-Si film are formed, while at the same time, part of the a-Si film is removed.
Owing to such a construction, the number of the photo-masks for use in photolithographic technology can be made three.
Moreover, the source wiring is covered with the transparent conductive film which is the same material as that of the pixel electrode, thereby to form a structure in which the whole substrate is protected from external static electricity etc. It is also allowed to form a structure in which a protective circuit is formed of the transparent conductive film. Owing to such a construction, the generation of the static electricity which is ascribable to the friction between a manufacturing apparatus and the insulator substrate can be prevented during a manufacturing process. In particular, TFTs etc. can be protected from the static electricity which appears during the rubbing of liquid crystal orientation processing that is performed in the manufacturing process.
The construction of an invention disclosed here in this specification consists in:
a semiconductor device having a gate wiring, a source wiring, and a pixel electrode, characterized by comprising:
the gate wiring 102 which is formed on an insulating surface;
an insulating film 104 which is formed on said gate wiring;
an amorphous semiconductor film 114 which is formed on said insulating film;
a source region 115 and a drain region 116 which are formed on said amorphous semiconductor film;
the source wiring 117 or a electrode 118 which is formed on said source region or said drain region; and
the pixel electrode 119 which is formed on said electrode;
wherein one end face of said drain region 116 or said source region 115 lies substantially in register with an end face of said amorphous semiconductor film 114 and an end face of said electrode 118.
Besides, the construction of another invention consists in:
a semiconductor device having a gate wiring, a source wiring, and a pixel electrode, characterized by comprising:
the gate wiring 102 which is formed on an insulating surface;
an insulating film 104 which is formed on said gate wiring;
an amorphous semiconductor film 114 which is formed on said insulating film;
a source region 115 and a drain region 116 which are formed on said amorphous semiconductor film;
the source wiring 117 or a electrode 118 which is formed on said source region or said drain region; and
the pixel electrode 119 which is formed on said electrode;
wherein one end face of said drain region 115 or said source 116 region lies substantially in register with an end face 114 of said amorphous semiconductor film and an end face of said electrode 118, and the other end face thereof lies substantially in register with an end face of said pixel electrode 119 and the other end face of said electrode 118.
Also, the construction of another invention consists in:
a semiconductor device having a gate wiring, a source wiring, and a pixel electrode, characterized by comprising:
the gate wiring 102 which is formed on an insulating surface;
an insulating film 104 which is formed on said gate wiring;
an amorphous semiconductor film 114 which is formed on said insulating film;
a source region 115 and a drain region 116 which are formed on said amorphous semiconductor film;
the source wiring 117 or a electrode 118 which is formed on said source region or said drain region; and
the pixel electrode 119 which is formed on said electrode;
wherein said amorphous semiconductor film, and an amorphous semiconductor film which contains an impurity element bestowing the n-type are stacked below said source wiring 117.
Also, in each of the above constructions, the semiconductor device is characterized in that said source region and said drain region are made of an amorphous semiconductor film which contains an impurity element bestowing the n-type.
Also, in each of the above constructions, the semiconductor device is characterized in that said insulating film, said amorphous semiconductor film, said source region and said drain region are formed successively without being exposed to the atmospheric air.
Also, in each of the above constructions, the semiconductor device is characterized in that said insulating film, said amorphous semiconductor film, said source region or said drain region is formed by a sputtering process.
Also, in each of the above constructions, the semiconductor device is characterized in that, as shown in FIG. 2(D), said source region 115 and said drain region 116 are formed by the same mask as that of said amorphous semiconductor film 114 and said electrode 118. Alternatively, the semiconductor device is characterized in that said source region and said drain region are formed by the same mask as that of said source wiring 117.
Also, in each of the above constructions, the semiconductor device is characterized in that, as shown in FIG. 2(D), said source region 115 and said drain region 116 are formed by the same mask as that of said source wiring 117 and said pixel electrode 119.
Also, in each of the above constructions, owing to an etching step in FIG. 2(D), the semiconductor device has a construction where film thicknesses in those regions of said amorphous semiconductor film which are contiguous to said source region and said drain region are greater than a film thickness in that region of said amorphous semiconductor film which lies between the region contiguous to said source region and the region contiguous to said drain region; that is, a bottom gate structure of channel etching type.
Besides, the construction of an invention for realizing the above structure consists in:
a method of fabricating a semiconductor device characterized by comprising:
the first step of forming each gate wiring 102 by employing a first mask;
the second step of forming an insulating film 104 which covers the gate wiring;
the third step of forming a first amorphous semiconductor film 105 on said insulating film;
the fourth step of forming a second amorphous semiconductor film 106 which contains an impurity element bestowing the n-type, on said first amorphous semiconductor film;
the fifth step of forming a first electrically-conductive film 107 on said second amorphous semiconductor film;
the sixth step of forming a wiring 111 (source wiring and electrode) in such a way that said first amorphous semiconductor film, said second amorphous semiconductor film and the first conductive film are selectively removed by employing a second mask;
the seventh step of forming a second electrically-conductive film 112 which overlies said wiring 111 (source wiring and electrode) and said electrode in touch with them; and
the eighth step of forming a source region 115 and a drain region 116 made of said second amorphous semiconductor film, and a pixel electrode 119 made of the second conductive film, in such a way that part of said first amorphous semiconductor film 109, said second amorphous semiconductor film 110, said first conductive film 111 and said second conductive film 112 are selectively removed by employing a third mask.
Also, in the above construction, the method is characterized in that said second step through said fifth step are performed successively without exposure to the atmospheric air.
Also, in each of the above constructions, the method is characterized in that said second step through said fifth step are performed successively within an identical chamber.
Also, in each of the above constructions, said insulating film may well be formed by a sputtering process or a plasma CVD process.
Also, in each of the above constructions, said first amorphous semiconductor film may well be formed by a sputtering process or a plasma CVD process.
Also, in each of the above constructions, said second amorphous semiconductor film may well be formed by a sputtering process or a plasma CVD process.
Also, in each of the above constructions, the method is characterized in that said second conductive film is a transparent electrically-conductive film or an electrically-conductive film having a reflectivity.